It's all about air density
Two forces from the air shape every shot. Drag slows the ball down; lift, from its backspin, holds it up. Both grow with the air's density: the mass of air the ball has to push out of the way every second. Less dense air means less drag, so the ball keeps its speed longer and flies farther, even though it also gets a little less lift and flies a slightly lower, flatter line.
Carry doesn't grow quite as fast as the air thins. Fitted to golf's measured rules of thumb, our model has carry change with density to the power of −0.45. So 10% thinner air adds about 5% of carry, around 7 yards on a 150-yard 7-iron.
Altitude: the big one
Air pressure falls as you climb, about 3.5% every 1,000 feet near the ground, and the air's density falls with it. That adds about 1.7% of carry per 1,000 feet (golfers often round it to 2%). At a mile high, a 150-yard 7-iron flies about 14 yards farther: more than the gap between two clubs for most golfers. It's why regulars in Flagstaff, Reno or Denver club down.
Temperature: a few yards
Warm air is less dense than cold air: its molecules move faster and spread out. From 70°F to 90°F a drive gains about 4 yards; from a 45°F winter morning to a 105°F summer afternoon, a 7-iron gains about 9. The ball itself matters too. A cold ball is less lively off the face, which our model doesn't include, so a frosty morning costs a little more than the numbers here.
Humidity: the myth
Many golfers believe humid air is "heavy" and knocks the ball down. It's the other way round: a water molecule weighs less than the nitrogen and oxygen it replaces, so humid air is slightly less dense and the ball flies a touch farther. The effect is tiny: under half a percent from bone dry to soaking on a mild day, about 1% on a hot one. What really costs distance on muggy days is a wet ball, wet grass between the face and the ball, and soft fairways that stop it rolling.
What else changes how far it flies
- Wind matters far more than the air's density on a breezy day, and it depends on each hole's direction.
- Elevation change between tee and green: an uphill approach plays longer, a downhill one shorter.
- Firm or soft ground changes the roll, not the carry: desert fairways in summer run.
- Day-to-day air pressure moves density by only about 1%, a yard or two at most.
Examples
| Conditions | Carry | 7-iron | Driver |
|---|---|---|---|
| Sea level, mild day0 ft, 70°F, 50% humidity | 0.0% | 0 yds | 0 yds |
| Phoenix, July afternoon1100 ft, 108°F, 20% humidity | +5.1% | +8 yds | +12 yds |
| Las Vegas, winter morning2000 ft, 45°F, 35% humidity | +1.0% | +1 yds | +2 yds |
| Tucson, spring2600 ft, 80°F, 20% humidity | +5.2% | +8 yds | +12 yds |
| Reno, summer4500 ft, 85°F, 20% humidity | +9.0% | +14 yds | +21 yds |
| Flagstaff, summer7000 ft, 75°F, 40% humidity | +12.9% | +19 yds | +30 yds |
| Coastal course, cold and humid0 ft, 50°F, 90% humidity | -1.7% | -3 yds | -4 yds |
For a 150-yard 7-iron and a 230-yard drive at sea level on a mild day.
See it on your course today
Every course forecast on TeeGauge shows the carry change hour by hour, from the forecast temperature and humidity and the course's elevation. Heading somewhere higher? The altitude calculator compares two courses, and the club distance calculator builds the yardages for your whole bag.